The first electronic amplifier was called an electron relay, borrowing telegraph slang
When Lee de Forest's Audion tube began strengthening weak signals, nobody yet had the word amplifier for it. The only familiar signal booster was the telegraph relay, so engineers called the new device an electron relay. The Latin-derived term amplification, from a word meaning to enlarge, only caught on around 1915.
The need came from the telephone, patented in 1876. Telegraph lines had coped with distance by relays at intermediate stations, each one receiving a message and retransmitting it with fresh local power. Voice was harder, especially in both directions at once. In 1904 H. E. Shreeve at AT&T produced a workable telephone repeater, built from carbon-granule transmitters paired back to back with receivers, first tried on a line from Boston to Amesbury, Massachusetts. Mercury lamps were also tested as boosters, without much luck.
De Forest's triode of 1906 made amplification fully electronic, and the first amplifiers followed around 1912. The consequences were enormous: long-distance calls, public address systems, radio broadcasting, films with sound, practical recording, radar, television and the earliest computers all depended on it. For half a century nearly every consumer electronic gadget ran on vacuum tubes.
Early designs were noisy and unstable, with distortion usually around 5 percent. Much of the theory was worked out at Bell Telephone Laboratories between the 1920s and 1940s, and the key trick came in 1934, when Harold Black introduced negative feedback, feeding part of the output back against the input. It sacrificed some gain but slashed distortion. Harry Nyquist and Hendrik Bode added further advances.
Bell Labs also produced the successor. John Bardeen and Walter Brattain built the first working transistor in 1947, William Shockley devised the junction version in 1948, and Mohamed Atalla and Dawon Kahng created the MOSFET in 1959, which, being endlessly shrinkable, is now the most widely used amplifier of all. Transistors displaced tubes during the 1960s and 1970s, enabling the transistor radio of 1954 and a flood of portable devices. Tubes survive mainly in radio transmitters, some guitar amps and high-end audiophile gear.
Source: Amplifier
